This invention relates to the field of photography, and more particularly to a film pack which accommodates instant picture film units.
An instant picture film unit film pack which produces no waste matters after image development and uses so-called mono-sheet type film units is described in Japanese Patent application Laid-Open No. 68828/1982 and is shown in FIGS. 1 and 2. The film pack comprises a box-shaped case body 2 which accommodates a predetermined number of film units 1, a depressing unit 5 having a depressing board 5' disposed within the case body 2 for biasing the film units 1 in the direction of arrow X (for exposure); and a light shielding cover 6 adapted to be discharged through a film unit discharging outlet 4, the outlet 4 forming a slit cut in one side of the case body 2. The case body 2 has an opening on its front, the opening being surrounded by a frame 3 and being used to expose the image forming region 21 of each film unit 1 as shown in FIGS. 3-a and 3-b.
The film unit 1 shown in the FIGS. 3-a and 3-b has a pod 23 at its front end which is positioned beside the film unit discharging outlet 4 when the film unit is in the film pack. The pod contains a processing solution for developing, etc., and is torn when pressed. The film unit further has a trap member 25 at its rear end. The image forming region 21 is surrounded by a frame 22 and is located between the trap member 25 and the pod 23. The trap member 25 incorporates a trap spacer 24 adapted to absorb excessive processing solution 33 which remains after the processing solution 33 has been spread between two sheets, namely, a photo-sensitive sheet 31 and a cover sheet 32.
The depressing unit in the conventional film pack serves to hold an image forming region 21 of a top film unit 1 at a suitable exposure position and to align a front end of the top film unit, where the pod 23 is located, with the slit-shaped discharging outlet 4.
FIG. 4 is a sectional view taken along line IV--IV in FIG. 1, showing how the film unit is discharged out of the film pack. After being exposed, the top film unit 1 in the film pack is pushed by a pushing unit 41 at a rear end of the film unit 1 where the trap member 25 for absorbing excessive processing solution is located. Accordingly, the front end of the film unit 1 where the pod 23 is located is fed between a pair of rolls 42. As a result, the pod is opened by the rolls and the processing solution is spread in the film unit to start developing while the film unit is discharged out of the camera. In order to prevent a plurality of film units from being discharged simultaneously, the clearance and position of the slit-shaped discharging outlet 4 is accurately determined according to the thickness and position of the pods 23 of the film units 1.
A picture taken with the above-described film units, film pack and camera sometimes lacks sharpness at a portion of a picture image forming region which is closer to the pod 23 at the front end of the film unit and/or at a portion of the image forming region which is closer to the trap member 25 at the rear end of the film unit 1. The inventors have found through analysis that this phenomenon is attributable principally to the fact that the film unit photosensitive surface is curved during a photographing operation. It has been also found that the lack of sharpness is more severe as the size of the film unit is increased. These difficulties may be overcome by using a camera lens system having a large depth of focus or by increasing the biasing force of the depressing plate 5' of the depressing unit 5.
In general, employment of a lens system having a large depth of focus results in an increase of the "F" value of the camera, thus not being desirable for an instant camera which normally already has a high "F" value.
On the other hand, increasing the elasticity or biasing force of the depressing unit 5 (FIG. 2) in the film pack and thus the depressing plate 5' as applied to the top film unit 1 so as to forcibly reduce the curvature of the top film unit also creates problems. Specifically, even if the biasing force is increased, the curvature of the top film unit is not reduced to the intent expected or required, and the force of friction between the top film unit 1 and the film pack opening frame 3 is excessively increased which obstructs smooth discharging of the top film unit. In addition, the increased frictional force increases the possibility of accidentally breaking and opening a pod of one of the lower ordered film units.
If the depressing plate 5' is brought into contact only with the image forming region 21 of the film units 1 as shown in FIG. 5 to increase the biasing force of the depressing plate, image sharpness is improved to some extent. However, in this case, the front end of the film unit 1, where the pod 23 is located, is shifted from the slit-shaped discharging outlet 4 of the film pack, and accordingly, the front end of the top film unit to be discharged is sometimes caught by the discharging outlet 4; that is, it is difficult to smoothly discharge the top film unit 1.